The subject invention relates to asphalt-based waterproof roofing membranes used in multi-ply asphalt-based commercial roofing systems and, in particular, to a prefabricated asphalt-based waterproof roofing membrane for use in a multi-ply asphalt-based commercial roofing system, e.g. a cap sheet that forms the exposed layer of a multi-ply built-up roofing system, that is manufactured at a factory to have a highly reflective upper surface to meet EPA Energy Star requirements.
Asphalt-based waterproof roofing membranes, such as cap sheets, are currently manufactured in a process that includes several major process steps. The process steps for producing these black asphalt-based waterproof roofing membranes include: saturating a reinforcing substrate with asphalt (bitumen), typically an oxidized or modified asphalt (bitumen); building up layers of asphalt on both major surfaces of the reinforcing substrate until the asphalt saturated and coated reinforcing substrate formed attains a desired thickness; applying granules, release agents or release films, or a combination of granules and release agents or release films to at least one major surface of the asphalt-based waterproof roofing membrane; winding the finished asphalt-based waterproof roofing membrane into a roll; and packaging the roll of asphalt-based waterproof roofing membrane for storage and shipment to a job site. The process steps of saturating the reinforcing substrate with black asphalt, e.g. an oxidized or modified asphalt, and building up layers of asphalt on both major surfaces of the reinforcing substrate may occur simultaneously. Typically, the reinforcing substrate used in the asphalt-based waterproof roofing membrane is a non-woven fiberglass mat, a reinforced fiberglass mat, a non-woven polyester mat, a reinforced polyester mat, a veiled scrim of various fiber combinations, or a laminated composite of two or more of the preceding reinforcing substrates that provide the asphalt-based waterproof roofing membrane with the necessary strength and flexibility.
In a typical manufacturing process, the reinforcing substrate is passed through a saturator/coater where the reinforcing substrate is saturated and coated with asphalt at temperatures from 300 to 425° F. The asphalt typically contains asphalt and mineral fillers and may contain modifiers, such as thermoplastics [Amorphous Polypropylene (APP)], rubbers [Styrene-Butadiene-Styrene (SBS)], and other polymers, antioxidants, resins, oils, etc. Where the saturator and coater units are separate, the asphalts used in the saturator unit to saturate the reinforcing substrate and in the coater unit to coat the reinforcing substrate and build up the thickness of the asphalt saturated and coated substrate may have the same composition or different compositions.
The reinforcing substrate is typically saturated and coated with asphalt by dipping the reinforcing substrate into a tank of the asphalt or by spreading asphalt over the top surface of the substrate as it passes through a coater. Squeeze rollers and other rollers in the coater apply the asphalt to the bottom surface of the sheet and distribute the asphalt evenly over the top and bottom surfaces of the reinforcing substrate to form built up layers of asphalt on the top and bottom surfaces of the reinforcing substrate.
After passing through the saturator/coater unit or the separate saturator and coater units, surfacing materials are typically adhered to both the top and bottom surfaces of the asphalt saturated and coated reinforcing substrate. In some processes, the asphalt saturated and coated reinforcing substrate may pass through a cooling unit where the asphalt saturated and coated reinforcing substrate is cooled prior to applying surfacing materials to the asphalt saturated and coated reinforcing substrate. Typically, the surfacing materials are applied to the asphalt saturated and coated reinforcing substrate by first passing the asphalt saturated and coated reinforcing substrate through a top surfacing unit. In the top surfacing unit, granules or other surfacing materials are applied to the top surface of the asphalt saturated and coated reinforcing substrate. With the desired surfacing material(s) applied to the top surface of the asphalt saturated and coated reinforcing substrate, the asphalt saturated and coated reinforcing substrate passes over a first press drum where the surfacing materials applied to the top surface of the asphalt saturated and coated reinforcing substrate are pressed into the asphalt layer on the top surface of the asphalt saturated and coated reinforcing substrate to assure good adhesion between the surfacing materials and the asphalt layer. As the asphalt saturated and coated reinforcing substrate passes over the first press drum, the asphalt saturated and coated reinforcing substrate is flipped simultaneously with the pressing operation so that the bottom surface of the asphalt saturated and coated reinforcing substrate is facing upward. This permits the application of surfacing materials (such as sand, other minerals (e.g. mica, talc, etc.), chemical release agents, and/or polymeric films) to the bottom surface of the asphalt saturated and coated reinforcing substrate by a bottom-surfacing unit. The asphalt saturated and coated reinforcing substrate then passes over a second press drum where the surfacing materials applied to the bottom surface of the asphalt saturated and coated reinforcing substrate are pressed into the asphalt layer on the bottom surface of the asphalt saturated and coated reinforcing substrate to assure good adhesion between the surfacing materials and the asphalt layer. The second press drum returns the asphalt saturated and coated reinforcing substrate to its normal orientation.
After the application of the surfacing materials to the top and bottom surfaces of the asphalt saturated and coated reinforcing substrate, the surfaced asphalt saturated and coated reinforcing substrate is cooled rapidly by water-cooled rolls and/or water sprays. The surfaced asphalt saturated and coated reinforcing substrate is then passed through a drying section where the surfaced asphalt saturated and coated reinforcing substrate is typically air dried to finish the manufacture of the asphalt-based waterproof roofing membrane. The finished asphalt-based waterproof roofing membrane is then fed through a looper or accumulator section to permit the continuous movement of the finished asphalt-based waterproof roofing membrane during the cutting and winding operation where the finished asphalt-based waterproof roofing membrane is cut into selected lengths and wound into rolls for packaging, storage, and shipment to a job site.
The ever increasing consumption of energy to cool buildings, coupled with global and regional environmental warming issues, has caused a conversion in contemporary roofing technologies to roofing with more reflective top surfaces so that the roofing better reflects solar radiation to thereby reduce the amount of solar radiation absorbed by the roofing and the amount of energy required to cool buildings. Contemporary roofing technologies typically increase the reflectivity of the top surface of the roofing by making the top surface (the exposed surface) of the roofing white.
Due to their irregular granular top surfaces and the intergranule spaces that reveal the black light-absorbing asphalt surfaces to which the granules are adhered, asphalt-based waterproof roofing membranes, such as cap sheets, currently on the market do not meet EPA Energy Star reflective requirements as measured by ASTM standard E-903—Standard Test Method for Solar Absorptance, Reflectance, and Transmission of Materials Using Integrating Spheres. The current technology used at the job site to upgrade asphalt-based waterproof roofing membranes and provide these roofing membranes with more reflective top surfaces involves covering the exposed surfaces of the roofing membranes with a reflective coating at the job site. This procedure leads to several problems: a waiting period of up to 30 days before the coating can be applied to the top surface of the membrane; the cost of and time required to clean the top surface of the membrane before applying the coating to the top surface of the membrane; the cost of and time involved in the labor intensive application of the coating to the top surface of the membrane; the quality and/or consistency of the application of the coating to the top surface of the membrane which is dependent on the skill and conscientiousness of the laborer; the limited service life of such coatings on the top surface of the membrane; and the requirement of periodic maintenance and reapplication of the coating to the top surface of the membrane. The problems associated with applying white coatings at the job site to the top surfaces of asphalt-based waterproof roofing membranes, plus the ease with which single-ply roofing membranes, such as polyvinyl chloride and thermoplastic olefin single-ply roofing membranes, can be made from white compounds, have contributed to market shifts away from multi-ply asphalt-based commercial roofing systems to single-ply membrane roofing systems.